Time Division Duplex (TDD) is a duplexing mode of a communication system, in which different time slots of the same frequency channel (i.e., carrier) are used for both the uplink communication and the downlink communication between a base station (BS) and a mobile station to separately receive and transfer information.
In a TDD system, an uplink Sounding Reference Symbol (SRS) is used for the BS to schedule uplink resources for a terminal. The BS configures an uplink SRS for the terminal, and the terminal transmits the SRS to the BS. The BS acquires uplink information as reference information for scheduling uplink resources for the terminal according to the received uplink SRS. The BS sends the uplink information to the terminal, and the terminal implements uplink data transfer by utilizing the uplink information.
The uplink information includes such information as Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI), Modulation and Coding Scheme (MCS), Rank indicator (RI) and so on. The terminal measures downlink channel information, and feeds back such information as relevant CQI, PMI and RI to the BS by utilizing an uplink control channel or an uplink data shared channel. The BS determines a precoding matrix to be used by the terminal according to the downlink PMI and RI. The BS queries corresponding tables of the CQI and MCS to obtain the MCS level of the terminal according to the downlink CQI, and notifies the terminal of its transmission format in a downlink control channel.
In the TDD system, because reciprocality exists between uplink and downlink channel information, the response of an uplink channel is the same as that of a downlink channel, but the interference of an uplink receiver side is different from that of a downlink receiver side.
When the BS receives information, interference information includes uplink transmission information of a terminal in a neighboring cell and downlink transmission information of a remote BS; when the terminal receives information, interference information includes downlink transmission information of a BS in a neighboring cell.
Two information scheduling methods exist for traditional TDD system.
In a first method, a terminal sends SRS information to a BS, and the SRS information received by the BS end is as follows:Y=h*s+n 
In the above formula, Y is received information of the BS end, h is an uplink channel response, s is an SRS symbol, and n is a noise of the BS receiver, which includes uplink reception interference information and a background thermal noise.
For an uplink channel, the BS receives the SRS sent by the terminal, and calculates the information-to-interference ratio for the uplink channel with a formula as follows:
      SINR    u    =                                        h                          2            ⁢                                  s                          2                                              x          U                            2      
In the above formula, ∥h∥2 is a channel gain, ∥s∥2 is a power for transmitting the SRS, and ∥xU∥2 is an uplink interference power measured by the BS, which includes the uplink reception interference information and the background thermal noise. The BS uses the information-to-interference ratio for the uplink channel of the terminal as reference information for scheduling uplink resources for the terminal.
For a downlink channel, the pilot information of the terminal receiver is as follows:Y=h*s+n 
In the above formula, Y is the received information of the terminal, h is the uplink channel response, s is the SRS symbol, and n is the noise of the terminal receiver, which includes the uplink reception interference information and the background thermal noise.
The terminal calculates the information-to-interference ratio for the downlink channel according to received downlink pilot information with a formula as follows:
      SINR    D    =                                        h                          2            ⁢                                  s                          2                                              x          D                            2      
In the above formula, ∥h∥2 is the channel gain, ∥s∥2 is the power for transmitting the SRS, and ∥xD∥2 is the downlink interference power measured by the terminal, which includes the downlink reception interference information and the background thermal noise. The terminal calculates a downlink channel quality according to the information-to-interference ratio and feeds back it to the BS, and the BS uses the downlink channel quality as reference information for scheduling downlink resources for the terminal.
However, such method causes a problem that the information amount to be fed back by the uplink channel is enormous. This is due to that in current TDD systems the uplink channel and the downlink channel are in different frequency bands and thus have different channel responses, and during downlink scheduling, the terminal needs to feed back the information received through the downlink channel to the BS through the uplink channel. Consequently, the problem of feeding back the enormous amount of information by the uplink channel is caused.
In light of this, another mode is presented in the prior art; i.e., the information-to-interference ratio for the uplink channel is used as reference information for scheduling downlink resources for a terminal.
First, a BS receives SRS information, and calculates the information-to-interference ratio for the uplink channel according to the power of the SRS and the power of uplink interference; i.e., the information-to-interference ratio for the uplink channel equals a product of ∥h∥2 and ∥s∥2 divided by ∥xU∥2. The formula is as follows:
      SINR    u    =                                        h                          2            ⁢                                  s                          2                                              x          U                            2      
In the above formula SINRU is the information-to-interference ratio for the uplink channel, ∥h∥2 is the channel gain of the pilot information, ∥s∥2 is the power for transmitting the pilot information, the product of ∥h∥2 and ∥s∥2 is the power of the pilot information, and ∥xU∥2 is the uplink interference power measured by the BS, which includes the uplink reception interference information and the background thermal noise. The BS uses the information-to-interference ratio for the uplink channel of the terminal as reference information for scheduling uplink resources for the terminal, and the BS also uses the information-to-interference ratio for the uplink channel of the terminal as reference information for scheduling downlink resources for the terminal.
During uplink scheduling, the BS uses the information-to-interference ratio for the uplink channel of the terminal as reference information for scheduling uplink resources for the terminal. the BS also uses the information-to-interference ratio for the uplink channel of the terminal as reference information for scheduling downlink resources for the terminal, which reduces the processes of feeding back the downlink channel information to the BS.
The method reduces information scheduling processes by utilizing the reciprocality of TDD channels, and solves the problem of feeding back the enormous amount information by the uplink channel. However, the BS does not take into account the interference information of the downlink channel during the downlink scheduling, but rather taking the interference information of the uplink channel as reference information for scheduling uplink resources for the terminal in scheduling the downlink channel. The uplink interference information and the downlink interference information are different, which causes that the information scheduling quality of the downlink channel is not accurate, reducing the transmission throughput of the downlink channel.
The BS does not take into account the interference information of the downlink channel during the downlink scheduling, but rather taking the interference information of the uplink channel as reference information for scheduling uplink resources for the terminal in scheduling the downlink channel. The uplink interference information and the downlink interference information are different, which causes that the information scheduling quality of the downlink channel is not accurate, reducing the transmission throughput of the downlink channel.